The present invention relates to a method and apparatus for recording and optically reproducing X-ray images on a recording material, and more particularly, to such a method and apparatus wherein the recording material is disposed in an ionization chamber filled with a gas which is ionizable by X-rays, a high voltage is applied to electrodes in the ionization chamber, the X-rays to be recorded are passed into the ionization chamber, the recording material is heated until a deformation image is formed according to the charge distribution produced during irradiation due to the ionization of the gas, and the deformation image is cooled and fixed.
X-ray images are, to a large extent, recorded on photographic X-ray films and plates, in which a photoconducting layer, preferably a selenium layer charged prior to exposure, is partially discharged by X-rays, and the remaining charge image is made visible by means of a toner. Selenium layers, however, have a relatively poor sensitivity to X-rays.
A known recording technique (German Pat. No. 1,497,093) uses photoelectrons which are produced in a photocathode which is sensitive to X-rays, e.g., made of lead. In an electric field within a chamber filled with an ionizable gas these photoelectrons are accelerated toward a dielectric film sheet. For developing the charge image on the film sheet by means of a toner, the ionization chamber is opened and the film sheet is removed. The sensitivity to X-rays is increased when the absorption of the X-ray quanta takes place in an ionizable gas, such as xenon, under positive pressure, instead of in the lead cathode. In practice, opening of the ionization chamber is unfavorable, since it always involves losses of gas and time. In order to prevent such losses, it is known from German Offenlegungsschrift No. 2,433,766 to transfer charge patterns through an insulating plate having inserted conducting pins to a dielectric charge carrier material outside the chamber. In this method, however, the quality of the image is impaired on account of a charge equalization between the closely spaced pins and also due to a capacitive interaction between the pins. In addition, special measures must be taken to ease the pressure acting on the pin plate which is sensitive to mechanical stresses.
In accordance with another known method (U.S. Pat. No. 3,842,801) the charge pattern produced on the dielectric sheet is developed with a toner powder, while the sheet is still in the ionization chamber. Thus, the access time is reduced, but the ionization chamber may easily get soiled and it must still be opened after each recording.
In the process disclosed in German Offenlegungsschrift No. 2,436,894, a thermoplastic recording layer is placed on a transparent electrode in an ionization chamber and is irradiated by X-rays. A high voltage is applied to the electrodes of the ionization chamber, which is filled with xenon under positive pressure, and subsequently X-rays are passed into the partly transparent chamber. Thus, a charge image is produced on the thermoplastic surface. The thermoplastic material is then heated until a deformation image is formed and is cooled down again to fix the image. Using a schlieren optical system positioned behind the chamber, the deformation image is shown on a screen. Thermal developing of the deformation image without a developer substance is a clean procedure which is accomplished in only a few seconds, so that X-ray images may be rapidly recorded and reproduced. A cyclic operation, in which several successive recordings are made and the respective deformation images are erased without having to open the chamber after each fixing of the deformation image is, however, not provided for in this process.